1. Field of the Invention
The present invention relates to a large-capacity optical router that exchanges data traffic such as Internet protocol (IP) packets, Ethernet frames, etc., at high speed in units of optical frames, and more particularly to a large-capacity optical router using an electric buffer.
2. Description of the Related Art
Generally, with the increased demand of data services such as Internet, moving picture, video on demand (VOD), etc., large-capacity data traffic in the range of several hundred gigabits/second (Gb/s) to several terabits/second (Tb/s) is produced in a network. In order to perform a switching or routing of such data traffic, a large-capacity router/switch having a capacity of several hundred Gb/s to several Tb/s is required.
Conventional large-capacity IP routers are constructed by connecting numerous small-capacity IP routers together. In this type of IP router, 50˜60% of the whole capacity is used for the mutual connection of the small-capacity IP routers. This causes a waste of bandwidth and an abrupt increase of the number of IP routers according to a required capacity. Two conventional methods have been used to construct such large-capacity routers.
FIG. 1 is a diagram illustrating the construction of a conventional all optical router, which will be used to discuss the first method for constructing the large-capacity router.
As illustrated in FIG. 1, optical data is exchanged through a space switch 14 composed of on-off gate switches 14-3. Any collision occurring in the optical data is prevented using a variable wavelength converter and an optical-fiber delay-line buffer 16. In addition, the optical data is switched using a variable wavelength converter and a wavelength router such as an N×N arrayed waveguide grating (AWG). Data collision is prevented through use of an optical-fiber delay line.
The second method is implemented by a large-capacity IP router adopting an interface of a speed over 10 Gb/s. According to this method, headers of input packets are recognized by packets, and the packet routing/switching is performed by driving an electric switch. Collision among the packets is prevented through an electric buffer. Using this method, a large-capacity IP router has been developed as a kind of terabit router.
In the all optical router of FIG. 1, an optical-fiber delay line is used to prevent collision among the optical data due to the absence of an optical memory. However, as the exchange capacity of optical routers increases and the length of optical data becomes long, the length of the optical-fiber delay line may reach several tens to several hundreds of kilometers, and this causes the size of the system to be enlarged and the complexity of the system is greatly increased.
It is also note that since the optical-fiber delay line uses the effect of time delay of an optical signal in the optical fiber, the system control becomes very difficult. The signal levels of the optical data also become different to properly detect due to loss or attenuation occurring in the optical fiber. In addition, most all optical routers use many variable wavelength converters for the switching or buffering. The variable wavelength converter is generally composed of a variable wavelength laser and a plurality of semiconductor optical amplifiers (SOAs). These added components cause the manufacturing cost to increase.
Also, the stabilization speed of the variable wavelength laser is very slow, i.e., in the range of several to several tens of milliseconds (ms), and thus it is not suitable for an optical router. In addition, in the all optical router, signal performance monitoring and signal regeneration are also difficult.
The all optical router of FIG. 1 uses many optical couplers. This causes a large path loss. In case of the electric IP router, since the packet forwarding is performed by recognizing the headers of the packets, there is a great difficulty in processing high-speed packets of 10 Gb/s. This has limited the interface to speeds of less than 40 Gb/s.
According to the conventional technology, forwarding speeds of 15 Mp/s and 60 Mp/s are required for processing 64-byte packets having speeds of 10 Gb/s and 40 Gb/s, respectively. Also, since not only add/drop packets but also path-through packets should be processed, the processing burden of the router greatly increases. This causes an inefficient use of the processing capacity.
While a high-speed electric switch can be used in the large-capacity IP router, such electric switches have limitations in speed and scalability. Also, numerous (e.g., several tens) large-capacity routers are needed for a large-capacity node, which requires a capacity of Th/s or more. This increases the complexity of the node and the node construction and the operation cost thereof.
Accordingly, there is a need in the art for improved large-capacity routers.